a period of warm, springlike weather occurring in the autumn—hence, figuratively, a late period of youthfulness—first used from 1639 onwards by the Anglican clergyman and historian Thomas Fuller (1608-1661)
USA, 1837—a short period of wintry weather occurring in autumn in the northern United States and in Canada—coined after ‘Indian summer’, from the fact that, because a squaw winter often precedes an Indian summer, they were seen as constituting a couple
The name ‘Indian summer’ (late 18th century) reflected the fact that to the Europeans living in the New World, this was a newly-discovered local phenomenon. But similar phenomena were already known in the Old World by various names.